As a process for preparing optically active 3-hydroxypentanenitrile, known is the optical resolution method (J. Org. Chem., 62, 9165 (1997)), wherein 3-acetoxynitrile compound which is a racemic body is hydrolyzed in the presence of thio-crown ether using a lipase derived from Pseudomonas cepacia. However, because this method is an optical resolution method, the yield of one enantiomer is low, that is at most 50%, and therefore is not satisfactory. Also, because the optical purity of the produced 3-hydroxypentanenitrile is low and thio-crown ether is added to improve the discrimination of an enzyme, industrial operation is difficult when considering cost and safety.
Also, a method for synthesizing 3-ketopentanenitrile, which is used as a raw material for preparing optically active 3-hydroxypentanenitrile in the present invention, is already known (WO94/21617). However, the obtained 3-ketopentanenitrile is known to be an unstable compound and to polymerize on its own (Aust. J. Chem., 44, 1263, (1991)). Therefore, 3-ketopentanenitrile is difficult to store over a long period of time and difficult to use from an industrial viewpoint.
As a result of intensive studies to develop an efficient process for preparing optically active 3-hydroxypentanenitrile, the present inventors have newly discovered an enzyme source, which has ability to stereoselectively reduce and convert 3-ketopentanenitrile into optically active 3-hydroxypentanenitrile. Thus, the present invention was achieved.
Furthermore, as a result of studies focusing on alkali metal salt of 3-ketopentanenitrile in order to avoid problems regarding storage due to unstableness of 3-ketopentanenitrile, a process for efficiently obtaining alkali metal salt of 3-ketopentanenitrile, which is a stable compound without problems regarding storage, has been discovered. Thus, the present invention was achieved.